This invention relates to control system for cyclic processes and to apparatus for performing such processes. In this context a "cyclic process" is a process which involves a repeated series of steps, and a particular process of manufacture or treatment may involve more than one such repeated series of steps, each of which is a cyclic stage in the whole cyclic process. In the cyclic processes with which the present invention is concerned, the series of steps in each cycle of any cyclic stage is initiated in sequence under the control of a train of pulses.
In the performance of a cyclic process, handling apparatus may be provided for performing a single cyclic stage or for performing two or more cyclic stages simultaneously. There will be particularly described in this Specification a method of formation of articles of glassware from molten glass by a "press-and-blow" or "blow-and-blow" technique, both of which techniques are cyclic processes involving a plurality of cyclic stages.
In the manufacture of glassware by the press-and-blow or blow-and-blow technique on a conventional glassware forming machine, gobs of molten glass are fed in groups of one, two or three into the machine and the gobs are each subjected to a process which involves approximately twenty separate and sequential steps (performed as a plurality of cyclic stages) and which result in the formation of an article of glassware from each gob. The gobs are handled mechanically throughout the process, the handling apparatus being operated by a set of fluid-operated, usually pneumatic, pistons and cylinders. The supply of fluid to the pistons and cylinders is controlled from a block of fluid valves, each of which operates in response to the movement of a respective actuating lever. The movement of a respective actuating lever. The movement of the actuating levers is controlled by a series of cam buttons mounted upon a timing drum which is rotated continuously.
It has also been proposed to form glassware by the press-and-blow or blow-and-blow technique using conventional handling apparatus for the gobs of molten glass, but providing an electronic rather than a mechanical means for controlling the operation of the fluid valves which control the flow of fluid into the pistons and cylinders of the handling apparatus. In this glassware forming system, each of the series of approximately twenty steps in the whole cyclic process is initiated under the control of a train of electrical pulses. As in the conventional process in which the steps are initiated from a timing drum, all the approximately twenty steps are performed in each cycle of the handling apparatus (referred to herein as a process cycle), and the whole process of forming a glass article from a gob extends over at least two cycles of operation of the handling apparatus, i.e. two process cycles.
It is a general object of the present invention to provide an improved control system for a cyclic process in which the steps of each cycle are initiated under the control of a train of pulses.
It is a further object of the present invention to provide a glassware forming system in which pulses for operating an electronic control of the handling apparatus are generated in a simple and reliable manner, the rate of generation of the pulses being automatically adjustable to compensate for variations in the rate at which gobs of glass are fed from the feeder mechanism to the handling apparatus.